Thru-line directional power sensor having microstrip coupler

ABSTRACT

Disclosed is a directional coupler having a coupler, a forward resistive attenuator, a reflected resistive attenuator, a forward compensation capacitor, and a reflected compensation capacitor. A forward coupler side arm and reflected coupler side arm of the coupler are configured to obtain a sample of forward energy and a sample of reflected energy from the coupler transmission line section. The forward resistive attenuator and reflected resistive attenuator are configured to attenuate the sample of forward energy and the sample of reflected energy. The forward compensation capacitor and the reflected compensation capacitor are configured to receive the attenuated sample of forward energy and the attenuated sample of reflected energy and produce a frequency-compensated sample of forward energy and a frequency-compensated sample of reflected energy.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the US National phase entry of International PatentApplication No. PCT/US2016/029897 filed Apr. 28, 2016, which claimspriority to U.S. Provisional Patent Application Ser. No. 62/154,105,filed Apr. 28, 2015, and titled THRU-LINE DIRECTIONAL POWER SENSORHAVING MICROSTRIP COUPLER, all of the above listed applications areincorporated by reference herein.

FIELD OF THE INVENTION

This application is directed to radio frequency (RF) power measurement.More specifically, to a thru-line directional RF power sensor having amicrostrip coupler.

BACKGROUND OF THE INVENTION

There are many applications within the radio communications industry,where it is desired to measure the power that is present within atransmission line structure. This increases the need for RF powersensors.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a directional coupleris provided. The directional coupler has a coupler, a forward resistiveattenuator, a reflected resistive attenuator, a forward compensationcapacitor, and a reflected compensation capacitor. The coupler iscomprised of a coupler transmission line section and a couplingstructure. The coupling structure has a coupled line with a couplinglength of D₁, the coupling structure also has a forward coupler side armelectrically connected to an upstream end of the coupled line, and areflected coupler side arm electrically connected to a downstream end ofthe coupled line.

The coupled line is coupled to the coupler transmission line section.The forward coupler side arm is configured to obtain a sample of forwardenergy from the coupler transmission line section using the coupledline, and the reflected coupler side arm is configured to obtain asample of reflected energy from the coupled transmission line sectionusing the coupled line. The forward coupler side arm is electricallyconnected to the forward resistive attenuator and configured to providethe sample of forward energy to the forward resistive attenuator. Theforward resistive attenuator is configured to attenuate the sample offorward energy, thereby producing an attenuated sample of forwardenergy, the forward resistive attenuator is electrically connected tothe forward compensation capacitor and configured to provide theattenuated sample of forward energy to the forward compensationcapacitor.

The forward compensation capacitor is configured to receive theattenuated sample of forward energy and produce a frequency-compensatedsample of forward energy. The reflected coupler side arm is electricallyconnected to the reflected resistive attenuator and configured toprovide the sample of reflected energy to the reflected resistiveattenuator. The the reflected resistive attenuator is configured toattenuate the sample of reflected energy, thereby producing anattenuated sample of reflected energy, the reflected resistiveattenuator is electrically connected to the reflected compensationcapacitor and configured to provide the attenuated sample of reflectedenergy to the reflected compensation capacitor. The reflectedcompensation capacitor is configured to receive the attenuated sample ofreflected energy and produce a frequency-compensated sample of reflectedenergy.

In another aspect of the invention, the directional coupler as set forthin claim 1, wherein the directional coupler is configured as afrequency-compensated shortline dual directional coupler

In another aspect of the invention, the coupling length (D₁) of thecoupled line is significantly less than λ/4, where λ is a wavelength ofan RF wave in the coupled line at a center frequency of the directionalcoupler.

In another aspect of the invention, the coupling length (D₁) of thecoupled line is between about λ/32 and λ/64.

In another aspect of the invention, the coupling length (D₁) of thecoupled line is about λ/42.

In another aspect of the invention, the coupling structure is amicrostrip on a printed circuit board (PCB).

In another aspect of the invention, the coupler transmission linesection can be a microstrip transmission line or a rigid airtransmission line.

In another aspect of the invention, the forward compensation capacitoris configured as a shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a feedthru shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a capacitive divider having a series capacitor and ashunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a capacitive divider having a series capacitor and afeedthru shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a capacitive divider having a first shunt capacitor anda series capacitor and a second shunt capacitor, wherein the secondshunt capacitor is a feedthru shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as: a shunt, a shunt feedthru, a series—shunt, aseries—shunt feedthru, or a shunt—series—shunt feedthru.

In another aspect of the invention, the reflected compensation capacitoris configured as a shunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as a feedthru shunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as a capacitive divider having a series capacitor and ashunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as a capacitive divider having a series capacitor and afeedthru shunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as: a shunt, a shunt feedthru, a series—shunt, aseries—shunt feedthru, or a shunt—series—shunt feedthru.

In another aspect of the invention, the reflected compensation capacitoris configured as a capacitive divider having a first shunt capacitor anda series capacitor and a second shunt capacitor, wherein the secondshunt capacitor is a feedthru shunt capacitor.

In another aspect of the invention, the forward resistive attenuator iscomprised of a chip attenuator, and the reflected attenuator iscomprised of a chip attenuator.

In another aspect of the invention, the forward resistive attenuator iscomprised of a chip attenuator and a lumped attenuator, and thereflected attenuator is comprised of a chip attenuator and a lumpedattenuator.

In another aspect of the invention, the forward compensation capacitorand the reflected compensation capacitor are configured to reduce thecoupling of the coupled line to the coupler transmission line section,thereby flattening a frequency response of the directional coupler.

In another aspect of the invention, the forward compensation capacitorand the reflected compensation capacitor are further configured toreduce a level of the frequency-compensated sample of forward energy anda level of the frequency-compensated sample of reflected energy throughvoltage division and reduce an impedance seen by a forward square-lawdetector and a reflected square-law detector.

In another aspect of the invention, the forward resistive attenuatorprovides isolation between the forward compensation capacitor and thecoupling structure, and the reflected resistive attenuator providesisolation between the reflected compensation capacitor and the couplingstructure, thereby preventing the forward compensation capacitor and thereflected compensation capacitor from degrading a directivity of thecoupler structure.

According to yet another aspect of the invention, a radio frequency (RF)power sensor is provided. The RF power sensor has a directional couplerand a power measurement circuit. The directional coupler is configuredto sample energy on a main transmission line and provides afrequency-compensated sample of forward energy and afrequency-compensated sample of reflected energy to the powermeasurement circuit. The frequency-compensated sample of forward energyis a sample of energy travelling in the forward direction on the maintransmission line, and the frequency-compensated sample of reflectedenergy is a sample of energy travelling in the reflected direction onthe main transmission line. The power measurement circuit is configuredto receive the frequency-compensated sample of forward energy and thefrequency-compensated sample of reflected energy and output a correcteddigitized forward power that is representative of the forward energytravelling on the main transmission line, and a corrected digitizedreflected power which is representative of the reflected energytravelling on the main transmission line.

The directional coupler comprises a coupler, a forward resistiveattenuator, a reflected resistive attenuator, a forward compensationcapacitor, and a reflected compensation capacitor. The coupler iscomprised of a coupler transmission line section and a couplingstructure. The coupling structure has a coupled line with a couplinglength of D₁, the coupling structure also has a forward coupler side armelectrically connected to an upstream end of the coupled line, and areflected coupler side arm electrically connected to a downstream end ofthe coupled line. The coupled line is coupled to the couplertransmission line section. The forward coupler side arm is configured toobtain a sample of forward energy from the coupler transmission linesection using the coupled line, and the reflected coupler side arm isconfigured to obtain a sample of reflected energy from the coupledtransmission line section using the coupled line.

The forward coupler side arm is electrically connected to the forwardresistive attenuator and configured to provide the sample of forwardenergy to the forward resistive attenuator. The forward resistiveattenuator is configured to attenuate the sample of forward energy,thereby producing an attenuated sample of forward energy, the forwardresistive attenuator is electrically connected to the forwardcompensation capacitor and configured to provide the attenuated sampleof forward energy to the forward compensation capacitor.

The forward compensation capacitor is configured to receive theattenuated sample of forward energy and produce a frequency-compensatedsample of forward energy. The reflected coupler side arm is electricallyconnected to the reflected resistive attenuator and configured toprovide the sample of reflected energy to the reflected resistiveattenuator. The reflected resistive attenuator is configured toattenuate the sample of reflected energy, thereby producing anattenuated sample of reflected energy, the reflected resistiveattenuator is electrically connected to the reflected compensationcapacitor and configured to provide the attenuated sample of reflectedenergy to the reflected compensation capacitor. The reflectedcompensation capacitor is configured to receive the attenuated sample ofreflected energy and produce a frequency-compensated sample of reflectedenergy.

In another aspect of the invention, the directional coupler isconfigured as a frequency-compensated shortline dual directional coupler

In another aspect of the invention, the coupling length (D₁) of thecoupled line is significantly less than λ/4, where λ is a wavelength ofan RF wave in the coupled line at a center frequency of the directionalcoupler.

In another aspect of the invention, the coupling length (D₁) of thecoupled line is between about λ/32 and λ/64.

In another aspect of the invention, the coupling length (D₁) of thecoupled line is about λ/42.

In another aspect of the invention, the coupling structure is amicrostrip on a printed circuit board (PCB).

In another aspect of the invention, the coupler transmission linesection can be a microstrip transmission line or a rigid airtransmission line.

In another aspect of the invention, the forward compensation capacitoris configured as a shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a feedthru shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a capacitive divider having a series capacitor and ashunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a capacitive divider having a series capacitor and afeedthru shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as a capacitive divider having a first shunt capacitor anda series capacitor and a second shunt capacitor, wherein the secondshunt capacitor is a feedthru shunt capacitor.

In another aspect of the invention, the forward compensation capacitoris configured as: a shunt, a shunt feedthru, a series—shunt, aseries—shunt feedthru, or a shunt—series—shunt feedthru.

In another aspect of the invention, the reflected compensation capacitoris configured as a shunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as a feedthru shunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as a capacitive divider having a series capacitor and ashunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as a capacitive divider having a series capacitor and afeedthru shunt capacitor.

In another aspect of the invention, the reflected compensation capacitoris configured as: a shunt, a shunt feedthru, a series—shunt, aseries—shunt feedthru, or a shunt—series—shunt feedthru.

In another aspect of the invention, the reflected compensation capacitoris configured as a capacitive divider having a first shunt capacitor anda series capacitor and a second shunt capacitor, wherein the secondshunt capacitor is a feedthru shunt capacitor.

In another aspect of the invention, the forward resistive attenuator iscomprised of a chip attenuator, and the reflected attenuator iscomprised of a chip attenuator.

In another aspect of the invention, the forward resistive attenuator iscomprised of a chip attenuator and a lumped attenuator, and thereflected attenuator is comprised of a chip attenuator and a lumpedattenuator.

In another aspect of the invention, the forward compensation capacitorand the reflected compensation capacitor are configured to reduce thecoupling of the coupled line to the coupler transmission line section,thereby flattening a frequency response of the directional coupler.

In another aspect of the invention, the forward compensation capacitorand the reflected compensation capacitor are further configured toreduce a level of the frequency-compensated sample of forward energy anda level of the frequency-compensated sample of reflected energy throughvoltage division and reduce an impedance seen by a forward square-lawdetector and a reflected square-law detector.

In another aspect of the invention, the forward resistive attenuatorprovides isolation between the forward compensation capacitor and thecoupling structure, and the reflected resistive attenuator providesisolation between the reflected compensation capacitor and the couplingstructure, thereby preventing the forward compensation capacitor and thereflected compensation capacitor from degrading a directivity of thecoupler structure.

Advantages of the present invention will become more apparent to thoseskilled in the art from the following description of the embodiments ofthe invention which have been shown and described by way ofillustration. As will be realized, the invention is capable of other anddifferent embodiments, and its details are capable of modification invarious respects.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

These and other features of the present invention, and their advantages,are illustrated specifically in embodiments of the invention now to bedescribed, by way of example, with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is an isometric view of a radio frequency (RF) power sensorhaving a frequency compensated shortline dual directional coupler inaccordance with an exemplary embodiment of the invention;

FIG. 2 is an overhead view of a lower portion of RF power sensor carrierbody in accordance with an exemplary embodiment of the invention;

FIG. 3 is an overhead view of an upper portion of RF power sensorcarrier body in accordance with an exemplary embodiment of theinvention;

FIG. 4 is a block diagram of RF power sensor in accordance with anexemplary embodiment of the invention;

FIG. 5 is an isometric view of a transmission line assembly of RF powersensor in accordance with an exemplary embodiment of the invention;

FIG. 6 is an overhead view of a transmission line assembly and couplerof RF power sensor in accordance with an exemplary embodiment of theinvention;

FIG. 7 is an overhead view of RF power sensor with upper portion ofcarrier body removed in accordance with an exemplary embodiment of theinvention;

FIG. 8 is an overhead view of the topside of the printed circuit boardof RF power sensor in accordance with an exemplary embodiment of theinvention;

FIG. 9 is an overhead view of the bottom side of the printed circuitboard of RF power sensor in accordance with an exemplary embodiment ofthe invention;

FIG. 10 is a block diagram of a frequency compensated shortlinedirectional coupler of RF power sensor in accordance with an exemplaryembodiment of the invention;

FIG. 11 is an overhead view of the frequency compensated shortlinedirectional coupler section of printed circuit board of RF power sensorin accordance with an exemplary embodiment of the invention;

FIG. 12 is an overhead view of the frequency compensated shortlinedirectional coupler section of printed circuit board of RF power sensorin accordance with an exemplary embodiment of the invention;

FIG. 13 is a block diagram for a power measurement circuit of RF powersensor in accordance with an exemplary embodiment of the invention;

FIG. 14 is a block diagram of a microcontroller of RF power sensor inaccordance with an exemplary embodiment of the invention;

FIG. 15 is a program stored in the memory and executed by the processorof RF power sensor directed to a method for the calculation of forwardand reflected power in accordance with an exemplary embodiment of theinvention;

FIGS. 16A-C are graphs illustrating coupling and directivity of acoupling length of coupling line in accordance with an exemplaryembodiment of the invention;

FIGS. 17A-E are schematics of various configurations of forwardcompensation capacitor of RF power sensor in accordance with anexemplary embodiment of the invention;

FIGS. 18A-E are schematics of various configurations of reflectedcompensation capacitor of RF power sensor in accordance with anexemplary embodiment of the invention;

FIGS. 19-20 are flow charts of a method of using RF power sensor inaccordance with an exemplary embodiment of the invention;

FIG. 21 is a block diagram of a channel power monitor in accordance withan exemplary embodiment of the invention;

FIG. 22 is a block diagram of an RF power metering system with the RFpower sensor in accordance with an exemplary embodiment of theinvention;

FIG. 23 is a flow chart showing a method for determining combiner lossin the RF transmission system using RF power metering system with RFpower sensor in accordance with an exemplary embodiment of theinvention;

FIG. 24 is a flow chart of a program for calculating loss in a combinerstored in memory and executed by processor of channel power meter of RFpower metering system having RF power sensor in accordance with anexemplary embodiment of the invention;

FIG. 25 is a flow chart showing a method for calculating VSWR in the RFtransmission system using RF power metering system with RF power sensorin accordance with an exemplary embodiment of the invention; and

FIG. 26 is a flow chart of a program for calculating VSWR in in the RFtransmission system stored in memory and executed by processor ofchannel power meter of RF power metering system having RF power sensorin accordance with an exemplary embodiment of the invention.

It should be noted that all the drawings are diagrammatic and not drawnto scale. Relative dimensions and proportions of parts of these figureshave been shown exaggerated or reduced in size for the sake of clarityand convenience in the drawings. The same reference numbers aregenerally used to refer to corresponding or similar features in thedifferent embodiments. Accordingly, the drawing(s) and description areto be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, is not limited to the precise valuespecified. In at least some instances, the approximating language maycorrespond to the precision of an instrument for measuring the value.Range limitations may be combined and/or interchanged, and such rangesare identified and include all the sub-ranges stated herein unlesscontext or language indicates otherwise. Other than in the operatingexamples or where otherwise indicated, all numbers or expressionsreferring to quantities of ingredients, reaction conditions and thelike, used in the specification and the claims, are to be understood asmodified in all instances by the term “about”.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, or that the subsequentlyidentified material may or may not be present, and that the descriptionincludes instances where the event or circumstance occurs or where thematerial is present, and instances where the event or circumstance doesnot occur or the material is not present.

As used herein, the terms “comprises”, “comprising”, “includes”,“including”, “has”, “having”, or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article or apparatus that comprises a list of elements is notnecessarily limited to only those elements, but may include otherelements not expressly listed or inherent to such process, method,article, or apparatus.

The singular forms “a”, “an”, and “the” include plural referents unlessthe context clearly dictates otherwise.

A “processor”, as used herein, processes signals and performs generalcomputing and arithmetic functions. Signals processed by the processorcan include digital signals, data signals, computer instructions,processor instructions, messages, a bit, a bit stream, or other meansthat can be received, transmitted and/or detected. Generally, theprocessor can be a variety of various processors including multiplesingle and multicore processors and co-processors and other multiplesingle and multicore processor and co-processor architectures. Theprocessor can include various modules to execute various functions.

A “memory”, as used herein can include volatile memory and/ornonvolatile memory. Non-volatile memory can include, for example, ROM(read only memory), PROM (programmable read only memory), EPROM(erasable PROM), and EEPROM (electrically erasable PROM). Volatilememory can include, for example, RAM (random access memory), synchronousRAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double datarate SDRAM (DDRSDRAM), and direct RAM bus RAM (DRRAM). The memory canalso include a disk. The memory can store an operating system thatcontrols or allocates resources of a computing device. The memory canalso store data for use by the processor.

A “disk”, as used herein can be, for example, a magnetic disk drive, asolid state disk drive, a floppy disk drive, a tape drive, a Zip drive,a flash memory card, and/or a memory stick. Furthermore, the disk can bea CD-ROM (compact disk ROM), a CD recordable drive (CD-R drive), a CDrewritable drive (CD-RW drive), and/or a digital video ROM drive (DVDROM). The disk can store an operating system and/or program thatcontrols or allocates resources of a computing device.

Some portions of the detailed description that follows are presented interms of algorithms and symbolic representations of operations on databits within a computer memory. These algorithmic descriptions andrepresentations are the means used by those skilled in the dataprocessing arts to most effectively convey the substance of their workto others skilled in the art. An algorithm is here, and generally,conceived to be a self-consistent sequence of steps (instructions)leading to a desired result. The steps are those requiring physicalmanipulations of physical quantities. Usually, though not necessarily,these quantities take the form of electrical, magnetic or opticalnon-transitory signals capable of being stored, transferred, combined,compared and otherwise manipulated. It is convenient at times,principally for reasons of common usage, to refer to these signals asbits, values, elements, symbols, characters, terms, numbers, or thelike. Furthermore, it is also convenient at times, to refer to certainarrangements of steps requiring physical manipulations or transformationof physical quantities or representations of physical quantities asmodules or code devices, without loss of generality.

However, all of these and similar terms are to be associated with theappropriate physical quantities and are merely convenient labels appliedto these quantities. Unless specifically stated otherwise as apparentfrom the following discussion, it is appreciated that throughout thedescription, discussions utilizing terms such as “processing” or“computing” or “calculating” or “determining” or “displaying” or“determining” or the like, refer to the action and processes of acomputer system, or similar electronic computing device (such as aspecific computing machine), that manipulates and transforms datarepresented as physical (electronic) quantities within the computersystem memories or registers or other such information storage,transmission or display devices.

Certain aspects of the embodiments described herein include processsteps and instructions described herein in the form of an algorithm. Itshould be noted that the process steps and instructions of theembodiments could be embodied in software, firmware or hardware, andwhen embodied in software, could be downloaded to reside on and beoperated from different platforms used by a variety of operatingsystems. The embodiments can also be in a computer program product whichcan be executed on a computing system.

The embodiments also relates to an apparatus for performing theoperations herein. This apparatus can be specially constructed for thepurposes, e.g., a specific computer, or it can comprise ageneral-purpose computer selectively activated or reconfigured by acomputer program stored in the computer. Such a computer program can bestored in a non-transitory computer readable storage medium, such as,but is not limited to, any type of disk including floppy disks, opticaldisks, CD-ROMs, magnetic-optical disks, read-only memories (ROMs),random access memories (RAMs), EPROMs, EEPROMs, magnetic or opticalcards, application specific integrated circuits (ASICs), or any type ofmedia suitable for storing electronic instructions, and eachelectrically connected to a computer system bus. Furthermore, thecomputers referred to in the specification can include a singleprocessor or can be architectures employing multiple processor designsfor increased computing capability.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems can also be used with programs in accordance with the teachingsherein, or it can prove convenient to construct more specializedapparatus to perform the method steps. The structure for a variety ofthese systems will appear from the description below. In addition, theembodiments are not described with reference to any particularprogramming language. It will be appreciated that a variety ofprogramming languages can be used to implement the teachings of theembodiments as described herein, and any references below to specificlanguages are provided for disclosure of enablement and best mode of theembodiments.

In addition, the language used in the specification has been principallyselected for readability and instructional purposes, and may not havebeen selected to delineate or circumscribe the inventive subject matter.Accordingly, the disclosure of the embodiments is intended to beillustrative, but not limiting, of the scope of the embodiments, whichis set forth in the claims.

As was stated above, there are many applications within the radiocommunications industry, where it is desired to measure the RF powerthat is present within a transmission line structure. While there havebeen many approaches to this requirement used throughout the years, theability to perform these measurements at low cost while maintaining highperformance has always been a challenge. High-performance directional RFpower sensors are difficult to design as low cost because of thechallenge of achieving good directivity and flat frequency response overa wide bandwidth. In order to meet these performance requirements, avery good directional coupler is required. Traditionally, the bestperforming directional couplers are coaxial and based on air-filledtransmission lines, which are relatively expensive to manufacture.Lower-cost directional couplers can be realized with planartechnologies, namely stripline and microstrip, but both havetraditionally had performance and manufacturing tradeoffs. For example,stripline is harder to manufacture than microstrip (and therefore moreexpensive). Further, stripline has challenges with getting signals fromthe top of the board to the inner layers. Stripline is also verydifficult to prototype in the lab due to the fact that the striplinestructure is constructed of properly and precisely laminated layers ofdielectric and copper.

Microstrip is very popular for use in RF circuits due to its excellentmanufacturability and compatibility with surface-mount components.Microstrip can also be easily prototyped in the lab, for quickevaluation and testing of designs. However, microstrip suffers from someperformance issues. For example, since microstrip is a non-homogeneousmedium, even and odd-mode phase velocities are different in microstrip,which leads to signal dispersion. This results in poor directivity andpoor bandwidth in microstrip couplers. These problems make microstripcouplers less suitable for RF power sensors, where coupling flatness andhigh directivity over a wide bandwidth are desired.

Designers have attempted to overcome the microstrip performance issuesin a number of ways. Common techniques for overcoming the different evenand odd-mode phase velocities include placing capacitors (either lumpedor printed) at the ends of the microstrip coupler. This technique worksfairly well when a single 2\14 coupling section is used, but bandwidthis generally limited to less than an octave. To increase bandwidth, somedesigns have multiple 2\14 coupling sections placed in series; howeverthe compensation of phase velocity becomes much more challenging acrossthese multiple sections.

The RF power sensor 100 of FIG. 1 avoids these microstrip performanceissues through a low-cost thru-line directional power sensor designbased on a directional coupler 300 that is a microstrip, short-line,frequency compensated, and dual-directional. In one exemplaryembodiment, the coupling length D₁ of coupled line 311 is about λ/42,which is much shorter than the typical λ/4 coupler, which results in adramatic reduction in the problem with different even and odd-mode phasevelocities and the resulting directivity is much improved. However, thetradeoff to the short-line microstrip directional coupler 300 is thatthe coupling is no longer flat, but increases with frequency at a rateof about 20 dB/decade. To overcome this problem, forward compensationcapacitor 330 and reflected compensation capacitor 335, containing shuntcapacitors, are added at the forward coupler side arm 312 and reflectedcoupler side arm 314 to reduce the coupling by about 20 dB/decade,resulting in a flat response. A forward resistive attenuator 320 isinserted between the forward coupler side arm 312 and forwardcompensation capacitor 330, and a reflected resistive attenuator 325 isinserted between the reflected compensation capacitor 335 and reflectedcoupler side arm 314, thus allowing the outputs to be well matched inorder to maintain good directivity. The signal from the forwardcompensation capacitor 330 is then presented to the forward square-lawdetector 410 and the signal from the reflected compensation capacitor335 is then presented to the reflected square-law detector 415 for powermeasurement.

The disclosed short-line microstrip coupler 300 avoids common problemswith 214 microstrip couplers. The resulting directivity is near about 30dB, but coupling increases between about 100-1000 MHz from about −44 dBto about −24 dB. The increasing coupling is compensated with shuntcapacitance, in the form of forward compensation capacitor 330 andreflected compensation capacitor 335, isolated from the coupler with anattenuator, in the form of forward resistive attenuator 320 andreflected resistive attenuator 325. In one embodiment, the shuntcapacitance of forward compensation capacitor 330 and reflectedcompensation capacitor 335 can be about 20 pF and the attenuator can beabout a 30 db attenuator. In some embodiments, forward compensationcapacitor 330 and reflected compensation capacitor 335 can take the formof a capacitive divider. The capacitive divider can be comprised of a 22pF series capacitor and a 220 pF shunt feed-thru capacitor. In someembodiments, this can further reduce the signal level to achieve anoverall coupling of about −83 dB that is flat from about 100 MHz toabout 1000 MHz. The capacitive divider can also reduce the drivingimpedance to the forward square-law detector 410 and reflectedsquare-law detector 415 to about 0.5 Ohms, which is ideal for gettingthe best temperature performance out of the forward square-law detector410 and reflected square-law detector 415. The feed-thru capacitor canalso allow the square-law detectors to be shielded in a metal can,thereby providing better isolation between the main transmission line600 and the diode detectors (forward square-law detector 410 andreflected square-law detector 415).

The disclosed design of the directional RF power sensor 100 allows forthe replacement of the expensive machined transmission line section,which is common in directional power sensors, with a low-cost microstripcoupler 305. The microstrip coupler 305 may be fabricated on an industrystandard substrate, such as FR-4. The microstrip coupler 305 andassociated circuitry can be assembled into a carrier body 200 to createa thru-line directional power sensor. The result is a smaller and lessexpensive directional power sensor with similar performance to the moreexpensive traditional design. In an exemplary embodiment, the full scaleforward power handling of RF power sensor 100 is 500 W forward and 50 Wreflected.

Turning to FIGS. 1-9, RF power sensor 100 has a carrier body 200 thatcontains a frequency compensated shortline directional coupler 300, apower measurement circuit 400, a printed circuit board (PCB) 500, and atransmission line assembly. In one exemplary embodiment, carrier body200 is plastic and rectangular in shape. Carrier body 200 has an upperportion 210, lower portion 220, left side 230, right side 235, bottom240, top 245, front 246, and back 255. Left side 230 is spaced apartfrom and located opposite right side 235. Front 246 and back 255 arespaced apart and located opposite each other, and span between left side230, right side 235, top 245 and bottom 240. Bottom 240 and top 245 arespaced apart and located opposite each other, and span between front246, back 255, left side 230, and right side 235.

Left side 230 has an upstream connector aperture 231, through whichupstream connector 232 passes. Right side 235 has a downstream connectoraperture 236, through which downstream connector 237 passes. Upstreamconnector 232 is electrically connectable to an upstream end 601 of maintransmission line 600. Downstream connector 237 is electricallyconnectable to a downstream end 602 of main transmission line 600.Bottom 240 has a port aperture 241 and a reset switch aperture 242. Portaperture 241 provides access to port 440, reset switch aperture 242provides access to reset switch 445, and LED aperture 243 providesaccess to LED 450. Port 440 can include a first port 441 and a secondport 442. In an exemplary embodiment, port 440 is an RS-485 interface,wherein first port 441 and second port 442 permit the daisy chaining ofmultiple RF power sensors 100.

The upper portion 210 has an upper portion forward cavity 211 with anupper portion forward cavity surface 212, and an upper portion rearcavity 215 with an upper portion rear cavity surface 216. In oneexemplary embodiment, upper portion forward cavity surface 212 and upperportion rear cavity surface 216 have a metallic coating. An upperportion dividing wall 218 divides the upper portion forward cavity 211from the upper portion rear cavity 215. The upper portion dividing wall218 runs from the left side 230 to the right side 235, parallel to thefront 246. The upper portion dividing wall 218 has a base 219.

The lower portion 220 has a lower portion forward cavity 221 with alower portion forward cavity surface 222, and a lower portion rearcavity 225 with a lower portion rear cavity surface 226. In oneexemplary embodiment, lower portion forward cavity surface 222 and lowerportion rear cavity surface 226 have a metallic coating. A lower portiondividing wall 228 divides the lower portion forward cavity 221 from thelower portion rear cavity 225. The lower portion dividing wall 228 runsfrom the left side 230 to the right side 235, parallel to the front 246.The lower portion dividing wall 228 has a base 229.

A first side 213 of the upper portion 210 contacts a first side 223 ofthe lower portion 220, when the upper portion 210 and the lower portion220 are assembled to form the carrier body 200.

Transmission line assembly 250 includes upstream connector 232,downstream connector 237, coupler transmission line section 251, andouter conductor 238. Upstream connector 232 and downstream connector 237are mounted on outer conductor 238. Upstream connector 232 anddownstream connector 237 are electrically connected to couplertransmission line section 251. More specifically, upstream connector 232is electrically connected to upstream section 252 of couplertransmission line section 251, and downstream connector 237 iselectrically connected to downstream section 253 of coupler transmissionline section 251. Outer conductor 238 is connectable to the couplersection 505 of PCB 500 using fasteners. In an exemplary embodiment,coupler transmission line section 251 can be a microstrip transmissionline, such as is shown in FIG. 6, or a rigid air transmission line, suchas is shown in FIG. 7. In an exemplary embodiment, the RF voltage oncoupler transmission line section 251 can be 158 Vrms at maximum forwardpower and 50 Vrms at maximum reflected power.

Forward square-law detector 410 and reflected square-law detector 415are very sensitive to stray energy. Accordingly, energy from couplertransmission line section 251 entering the rear cavity could potentiallyresult in erroneous output from forward square-law detector 410 andreflected square-law detector 415. Accordingly, some embodiments of RFpower sensor 100 include measures to reduce the amount of energy fromcoupler transmission line section 251 that can migrate to the forwardsquare-law detector 410 and reflected square-law detector 415.

In one exemplary embodiment, PCB 500 includes a via wall 340 thattravels from a topside 501 of PCB 500 to a bottom side 502 of PCB 500.Via wall 340 works in conjunction with the upper portion dividing wall218 and the lower portion dividing wall 228 to minimize the amount ofenergy travelling on coupler transmission line section 251 from enteringthe rear cavity formed by upper portion rear cavity 215 and lowerportion rear cavity 225.

More specifically, via wall 340 travels through PCB 500 and has a coppertrace on the topside 501 of PCB 500 and on the bottom side 502 of PCB500. Via wall 340 on the topside 501 contacts the base 219 of upperportion dividing wall 218, and via wall 340 on the bottom side 502contacts the base 229 of the lower portion dividing wall 228. Therefore,since the upper portion dividing wall 218 and lower portion dividingwall 228 are both coated in a metallic finish, via wall 340, upperportion dividing wall 218, and lower portion dividing wall 228 form ametallic barrier between the coupler transmission line section 251 andthe forward square-law detector 410 and reflected square-law detector415. PCB 500 can be constructed out of any standard PCB material, suchas FR-4, or higher-frequency printed circuit board materials offered byRogers or Arlon.

Further, in some exemplary embodiments of RF power sensor 100, themetallic coating on the upper portion rear cavity surface 216 and lowerportion rear cavity surface 226 also form a metallic barrier to helpprevent energy around RF power sensor 100 from interfering with theoperation of forward square-law detector 410 and reflected square-lawdetector 415.

In some exemplary embodiments of RF power sensor 100, a ground plane 530can be placed on the topside 501 of PCB 500 to help prevent energy fromsurrounding circuitry and traces from interfering with the operation offorward square-law detector 410 and reflected square-law detector 415.In some exemplary embodiments, ground plane 530 is present on thedetection section 510 of PCB 500 and absent on the coupler section 505of PCB 500.

Further, in some exemplary embodiments of RF power sensor 100, a shieldarea 520 is placed around forward square-law detector 410 and reflectedsquare-law detector 415 to help prevent energy from surroundingcircuitry from interfering with the operation of forward square-lawdetector 410 and reflected square-law detector 415. In the exemplaryembodiment shown in FIG. 6, shield area 520 is in the form of forwardcan 521 placed around forward square-law detector 410 and reflected can522 placed around reflected square-law detector 415. In anotherexemplary embodiment, forward square-law detector 410 and reflectedsquare-law detector 415 are located in the same can.

In some exemplary embodiments, coupler section 505 and detection section510 are located on separate PCBs 500, and in other exemplaryembodiments, coupler section 505 and detection section 510 are locatedon the same PCB 500. Further, coupler section 505 and detection section510 are separated by via wall 340.

Turning to FIGS. 4 and 7-14, FIG. 10 is a block diagram and FIGS. 11-12are a depiction of a section of PCB 500 containing a frequencycompensated shortline directional coupler 300 of RF power sensor 100.Directional coupler 300 samples the energy on main transmission line 600(RF voltage) and provides a frequency-compensated sample of energytravelling in the forward direction (sample of forward energy) and afrequency-compensated sample of energy travelling in the reflecteddirection (sample of reflected energy) to power measurement circuit 400.Power measurement circuit 400 receives the frequency-compensated sampleof forward energy and the frequency-compensated sample of reflectedenergy from directional coupler 300 and produces an output which isrepresentative of the forward energy travelling on main transmissionline 600 and an output which is representative of the reflected energytravelling on main transmission line 600. More specifically, powermeasurement circuit 400 outputs a corrected digitized forward powerwhich is representative of the forward energy travelling on maintransmission line 600, and a corrected digitized reflected power whichis representative of the reflected energy travelling on maintransmission line 600.

Directional coupler 300 has a coupler 305, a forward resistiveattenuator 320, reflected resistive attenuator 325, forward compensationcapacitor 330, and reflected compensation capacitor 335. Coupler 305 iselectrically connected to forward resistive attenuator 320 and reflectedresistive attenuator 325. Forward resistive attenuator 320 iselectrically connected to forward compensation capacitor 330. Reflectedresistive attenuator 325 is electrically connected to reflectedcompensation capacitor 335.

Coupler 305, coupling structure 310, forward resistive attenuator 320,and reflected resistive attenuator 325 are located on an upstream sideof via wall 340. Forward compensation capacitor 330 and reflectedcompensation capacitor 335 are located on a downstream side of via wall340. Forward resistive attenuator 320 provides isolation betweencoupling structure 310 and forward compensation capacitor 330. Forwardcompensation capacitor 330 would harm the directivity of couplingstructure 310, if forward resistive attenuator 320 did not isolatecoupling structure from forward compensation capacitor. Reflectedresistive attenuator 325 provides isolation between coupling structure310 and reflected compensation capacitor 335. Reflected compensationcapacitor 335 would harm the directivity of coupling structure 310, ifreflected resistive attenuator 325 did not isolate coupling structure310 from reflected compensation capacitor 335.

Directional coupler 300 is electrically connectable to the maintransmission line 600 through upstream connector 232 and downstreamconnector 237. Directional coupler 300 is also electrically connected tothe forward square-law detector 410 and reflected square-law detector415. The forward compensation capacitor 330 is electrically connected tothe forward square-law detector 410. The reflected compensationcapacitor 335 is electrically connected to the reflected square-lawdetector 415.

Coupler 305 has coupler transmission line section 251 and couplingstructure 310. Coupler transmission line section 251 is electricallyconnectable to coupling structure 310. Coupler transmission line section251 is electrically connectable to the main transmission line 600through upstream connector 232 and downstream connector 237. Whencoupler transmission line section 251 is electrically connected to themain transmission line 600, the energy flowing between the upstream end601 and downstream end 602 of main transmission line 600 passes throughcoupler transmission line section 251 of coupler 305.

Coupler transmission line section 251 is configured to couple withcoupling structure 310 through coupled line 311, when RF power ispresent on the coupler transmission line section 251. Coupler 305 isconfigured to obtain a sample of the energy on main transmission line600 (RF Voltage) using coupling structure 310 and provide a sample ofthe energy travelling in the forward direction to forward resistiveattenuator 320 and a sample of the energy travelling in the reflecteddirection to reflected resistive attenuator 325.

Coupling structure 310 has a coupled line 311, a forward coupler sidearm 312, and a reflected coupler side arm 314. Coupled line 311 iselectrically connected to forward coupler side arm 312 and coupled line311 is electrically connected to reflected coupler side arm 314.

More specifically, coupled line 311 has an upstream end 313 and adownstream end 315. A first end 312A of forward coupler side arm 312 iselectrically connected to the upstream end 313, and a second end 312B offorward coupler side arm 312 is electrically connected to forwardresistive attenuator 320. A first end 314A of reflected coupler side arm314 is electrically connected to the downstream end 315 of coupled line311, and a second end 314B of reflected coupler side arm 314 iselectrically connected to reflected resistive attenuator 325. Thebalance between coupling and directivity for a given coupling length D₁of coupled line 311 is illustrated in FIGS. 16A-C. In an exemplaryembodiment, the length of the coupled line 311, which is represented bythe coupling length D₁ in FIGS. 11-12, is less than λ/4. In anotherexemplary embodiment, the coupling length of coupled line 311, D₁, issignificantly less than λ/4. In further exemplary embodiment, thecoupling length of coupled line 311, D₁, can be between about λ/32 andλ/64. In another exemplary embodiment, the coupling length of coupledline 311, D₁, can be about λ/42.

λ is the wavelength of the RF wave in the coupled line 311 at the centerfrequency of directional coupler 300 of RF power sensor 100. In anexemplary embodiment, λ can be the wavelength in the coupled line 311 ofdirectional coupler 300 around 500 MHz (halfway between 100-1000 MHz).

Further, coupler transmission line section 251 runs parallel to coupledline 311. Coupler transmission line section 251 and coupled line 311 areseparated by a distance D₂. In an exemplary embodiment, distance D₂between coupler transmission line section 251 and coupled line 311 canbe between about 0.005 inches to about 0.015 inches. In anotherexemplary embodiment, distance D₂ between coupler transmission linesection 251 and coupled line 311 can be about 0.010 inches. In anotherexemplary embodiment distance D₂ between coupler transmission linesection 251 and coupled line 311 is selected such that the even-mode andodd-mode impedances are balanced, resulting in cancellation of thereflected wave on the forward coupler side arm 312 and cancellation ofthe forward wave on the reflected coupler side arm 314.

Coupled line 311 is configured to couple with coupler transmission line251, when RF power is present on the coupler transmission line section251, obtain a sample of the energy on main transmission line 600 (RFVoltage), provide the sample of energy travelling in the forwarddirection on main transmission line 600 to the forward coupler side arm312, and provide the sample of energy travelling in the reflecteddirection on main transmission line 600 to the reflected coupler sidearm.

The forward coupler side arm 312 is electrically connected to theforward resistive attenuator 320. The forward coupler side arm 312 isconfigured to provide the sample of energy travelling in the forwarddirection to the forward resistive attenuator 320. Accordingly, forwardcoupler side arm 312 is configured to receive the sample of energytravelling in the forward direction on main transmission line 600 fromcoupled line 311, and provide to forward resistive attenuator 320 thesample of energy travelling in the forward direction on maintransmission line 600 (sample of forward energy). In one exemplaryembodiment, the sample of energy travelling in the forward direction ofmain transmission line can, at maximum full scale power, have a voltagebetween 1 Vrms to 10 Vrms, from 100 MHz to 1000 MHz, and an attenuationof −44 dB to −24 dB, from 100 MHz to 1000 MHz.

The reflected coupler side arm 314 is electrically connected to thereflected resistive attenuator 325. The reflected coupler side arm 314is configured to provide the sample of energy travelling in thereflected direction on main transmission line 600 to the reflectedresistive attenuator 325. Accordingly, reflected coupler side arm 314 isconfigured to receive the sample of energy travelling in the reflecteddirection on main transmission line 600 from coupled line 311, andprovide to reflected resistive attenuator 325 the sample of energytravelling in the reflected direction on main transmission line 600(sample of reflected energy). In one exemplary embodiment, the sample ofenergy travelling in the reflected direction of main transmission linecan, at maximum full scale power, have a voltage between 320 mVrms to3.2 Vrms, from 100 MHz to 1000 MHz, and an attenuation of −44 dB to −24dB, from 100 MHz to 1000 MHz.

Forward resistive attenuator 320 receives the sample of energytravelling in the forward direction on main transmission line 600produced by coupler 305 (sample of forward energy). Forward resistiveattenuator 320 attenuates the sample of energy travelling in the forwarddirection (RF voltage) received from coupler 305 by setting the voltagelevel of the sample of forward energy to a level appropriate for theforward compensation capacitor 330. Forward resistive attenuator 320outputs the attenuated sample of forward energy to forward compensationcapacitor 330. Forward resistive attenuator 320 also provides isolationbetween the circuit components of the coupler 305 and the remainder ofthe circuit components of the RF power sensor 100, such as the forwardcompensation capacitor 330 and the power measurement circuit 400. In oneexemplary embodiment, the attenuated sample of forward energy can, atmaximum full scale power, have a voltage between 32 mVrms to 320 mVrms,from 100 MHz to 1000 MHz, and an attenuation of −74 dB to −54 dB, from100 MHz to 1000 MHz.

More specifically, forward resistive attenuator 320 receives the sampleof energy travelling in the forward direction on main transmission line600 produced by coupling structure 310 (sample of forward energy).Forward resistive attenuator 320 attenuates the sample of energytravelling in the forward direction (RF voltage) received from couplingstructure 310 by setting the voltage level of the sample of forwardenergy to a level appropriate for the forward compensation capacitor330. Forward resistive attenuator 320 outputs the attenuated sample offorward energy to forward compensation capacitor 330. Forward resistiveattenuator 320 also provides isolation between the circuit components ofthe coupler 305 and the remainder of the circuit components of the RFpower sensor 100, such as the forward compensation capacitor 330 and thepower measurement circuit 400.

Even more specifically, forward resistive attenuator 320 receives thesample of energy travelling in the forward direction on maintransmission line 600 produced by forward coupler side arm 312 (sampleof forward energy). Forward resistive attenuator 320 attenuates thesample of energy travelling in the forward direction (RF voltage)received from forward coupler side arm 312 by setting the voltage levelof the sample of forward energy to a level appropriate for the forwardcompensation capacitor 330. Forward resistive attenuator 320 outputs theattenuated sample of forward energy to forward compensation capacitor330. Forward resistive attenuator 320 also provides isolation betweenthe circuit components of the coupler 305 and the remainder of thecircuit components of the RF power sensor 100, such as the forwardcompensation capacitor 330 and the power measurement circuit 400.

Accordingly, forward resistive attenuator 320 is configured to receivethe sample of energy travelling in the forward direction (RF power) onmain transmission line 600 (sample of forward energy) and convert thesample of forward energy to an attenuated sample of forward energy (RFvoltage) representative of the forward energy travelling on maintransmission line 600.

Reflected resistive attenuator 325 receives the sample of energytravelling in the reflected direction on main transmission line 600produced by coupler 305 (sample of reflected energy). Reflectedresistive attenuator 325 attenuates the sample of energy travelling inthe reflected direction (RF voltage) received from coupler 305 bysetting the voltage level of the sample of reflected energy to a levelappropriate for the reflected compensation capacitor 335. Reflectedresistive attenuator 325 outputs the attenuated sample of reflectedenergy to reflected compensation capacitor 335. Reflected resistiveattenuator 325 also provides isolation between the circuit components ofthe coupler 305 and the remainder of the circuit components of the RFpower sensor 100, such as the reflected compensation capacitor 335 andthe power measurement circuit 400. In one exemplary embodiment, theattenuated sample of reflected energy can, at maximum full scale power,have a voltage between 10 mVrms to 100 mVrms, from 100 MHz to 1000 MHz,and an attenuation of −74 dB to −54 dB, from 100 MHz to 1000 MHz.

More specifically, reflected resistive attenuator 325 receives thesample of energy travelling in the reflected direction on maintransmission line 600 produced by coupling structure 310 (sample ofreflected energy). Reflected resistive attenuator 325 attenuates thesample of energy travelling in the reflected direction (RF voltage)received from coupling structure 310 by setting the voltage level of thesample of reflected energy to a level appropriate for the reflectedcompensation capacitor 335. Reflected resistive attenuator 325 outputsthe attenuated sample of reflected energy to reflected compensationcapacitor 335. Reflected resistive attenuator 325 also providesisolation between the circuit components of the coupler 305 and theremainder of the circuit components of the RF power sensor 100, such asthe reflected compensation capacitor 335 and the power measurementcircuit 400.

Even more specifically, reflected resistive attenuator 325 receives thesample of energy travelling in the reflected direction on maintransmission line 600 produced by reflected coupler side arm 314 (sampleof reflected energy). Reflected resistive attenuator 325 attenuates thesample of energy travelling in the reflected direction (RF voltage)received from reflected coupler side arm 314 by setting the voltagelevel of the sample of reflected energy to a level appropriate for thereflected compensation capacitor 335. Reflected resistive attenuator 325outputs the attenuated sample of reflected energy to reflectedcompensation capacitor 335. Reflected resistive attenuator 325 alsoprovides isolation between the circuit components of the coupler 305 andthe remainder of the circuit components of the RF power sensor 100, suchas the reflected compensation capacitor 335 and the power measurementcircuit 400.

Accordingly, reflected resistive attenuator 325 is configured to receivethe sample of energy travelling in the reflected direction (RF power) onmain transmission line 600 (sample of reflected energy) and convert thesample of reflected energy to an attenuated sample of reflected energy(RF voltage) representative of the reflected energy travelling on maintransmission line 600.

Forward resistive attenuator 320 and reflected resistive attenuator 325also allow the forward and reflected outputs (forward coupler side arm312 and reflected coupler side arm 314) of the coupler 305 to be wellmatched in order to maintain good directivity.

In one exemplary embodiment, forward resistive attenuator 320 andreflected resistive attenuator 325 each provide about 30 dB ofattenuation. In an exemplary embodiment, the 30 dB of attenuation cancome in the form of a 20 dB chip attenuator and a 10 dB lumpedattenuator. In an exemplary embodiment, the 10 dB lumped attenuator canbe in the form of three resistors.

When the coupling length D₁ of coupled line 311 is reduced significantlybelow λ/4, the coupling is no longer flat, but increases with frequencyat a rate of about 20 dB/decade. In one exemplary embodiment, theresulting directivity is around about 30 dB, but coupling increasesbetween about 100-1000 MHz from about −44 dB to about −24 dB.

To overcome this problem, forward compensation capacitor 330 andreflected compensation capacitor 335 are used to reduce the coupling byabout 20 dB/decade, resulting in a flat response from coupler 305. Insome embodiments, this can further reduce the signal level to achieve anoverall coupling of about −83 dB that is flat from about 100 MHz toabout 1000 MHz. This can also reduce the driving impedance to theforward square-law detector 410 and reflected square-law detector 415 toabout 0.5 Ohms.

Forward compensation capacitor 330 receives the attenuated sample offorward energy from forward resistive attenuator 320. Forwardcompensation capacitor 330 processes the attenuated sample of forwardenergy, and outputs the frequency-compensated sample of forward energyto forward square-law detector 410 of power measurement circuit 400. Inone exemplary embodiment, forward compensation capacitor 330 processesthe attenuated sample of forward energy by carrying out one or more offlattening the frequency response, reducing the signal level (voltagedivision), and reducing the impedance seen by forward square-lawdetector 410. All of these are beneficial for driving the forwardsquare-law detector 410 and reflected square-law detector 415 properly.In one exemplary embodiment, the frequency-compensated sample of forwardenergy can, at maximum full scale power, have a voltage of 9 mVrms andan attenuation of −85 dB.

Reflected compensation capacitor 335 receives the attenuated sample ofreflected energy from reflected resistive attenuator 325. Reflectedcompensation capacitor 335 processes the attenuated sample of reflectedenergy, and outputs the frequency-compensated sample of reflected energyto reflected square-law detector 415 of power measurement circuit 400.In one exemplary embodiment, reflected compensation capacitor 335processes the attenuated sample of reflected energy by carrying out oneor more of flattening the frequency response, reducing the signal level(voltage division), and reducing the impedance seen by reflectedsquare-law detector 415. In one exemplary embodiment, thefrequency-compensated sample of reflected energy can, at maximum fullscale power, have a voltage of 9 mVrms and an attenuation of −75 dB.

In an exemplary embodiment, forward compensation capacitor 330 can be ashunt capacitor 332. In another exemplary embodiment, the forwardcompensation capacitor 330 can be a series capacitor 331 and a shuntcapacitor 332 configured as a capacitive divider. In an exemplaryembodiment, the shunt capacitor 332 can be a feed-thru type capacitor,grounded to a shield area 520 of PCB 500. In an exemplary embodiment,the feed-thru type shunt capacitor 332 can be grounded to forward can521.

In an exemplary embodiment, reflected compensation capacitor 335 can bea shunt capacitor 337. In another exemplary embodiment, the reflectedcompensation capacitor 335 can be a series capacitor 336 and a shuntcapacitor 337 configured as a capacitive divider. In an exemplaryembodiment, the shunt capacitor 337 can be a feed-thru type capacitor,grounded to a shield area 520 of PCB 500. In an exemplary embodiment,the feed-thru type shunt capacitor 337 can be grounded to reflected can522.

The above configurations for forward compensation capacitor 330 andreflected compensation capacitor 335 are illustrated in FIGS. 17A-E forforward compensation capacitor 330 and FIGS. 18A-E for reflectedcompensation capacitor 335. FIG. 17A shows forward compensationcapacitor 330 in a shunt capacitor configuration using shunt capacitor332. FIG. 17B shows forward compensation capacitor 330 in a shuntfeedthru capacitor configuration using shunt capacitor 332 configured asa feedthru. FIG. 17C shows forward compensation capacitor 330 in aseries—shunt configuration using series capacitor 331 and shuntcapacitor 332. FIG. 17D shows forward compensation capacitor 330 in aseries—shunt feedthru configuration using series capacitor 331 and shuntcapacitor 332 configured as a feedthru. FIG. 17E shows forwardcompensation capacitor 330 in a shunt—series—shunt feedthruconfiguration using first shunt capacitor 332 a, series capacitor 331,and second shunt capacitor 332 b configured as a feedthru.

FIG. 18A shows reflected compensation capacitor 335 in a shunt capacitorconfiguration using shunt capacitor 337. FIG. 18B shows reflectedcompensation capacitor 335 in a shunt feedthru capacitor configurationusing shunt capacitor 337 configured as a feedthru. FIG. 18C showsreflected compensation capacitor 335 in a series—shunt configurationusing series capacitor 336 and shunt capacitor 337. FIG. 18D showsreflected compensation capacitor 335 in a series—shunt feedthruconfiguration using series capacitor 336 and shunt capacitor 337configured as a feedthru. FIG. 18E shows reflected compensationcapacitor 335 in a shunt—series—shunt feedthru configuration using firstshunt capacitor 337 a, series capacitor 336, and second shunt capacitor337 b configured as a feedthru.

FIG. 13 is a block diagram of power measurement circuit 400 of RF powersensor 100. Forward square-law detector 410 receives thefrequency-compensated sample of forward energy (RF voltage) from forwardcompensation capacitor 330 and outputs to forward analog gain stage 420a forward analog DC voltage representative of the forward energytravelling on main transmission line 600. Accordingly, forwardsquare-law detector 410 is configured to receive thefrequency-compensated sample of forward energy (RF voltage)representative of the forward energy travelling on main transmissionline 600, convert the frequency-compensated sample of forward energy toa forward analog DC voltage representative of the forward energytravelling on main transmission line 600, and provide the forward analogDC voltage to forward analog gain stage 420. In one exemplaryembodiment, the forward analog DC voltage output can, at maximum fullscale power, have a voltage of about 1 mV.

Reflected square-law detector 415 receives the frequency-compensatedsample of reflected energy (RF voltage) from reflected compensationcapacitor 335 and outputs to reflected analog gain stage 425 a reflectedanalog DC voltage representative of the reflected energy travelling onmain transmission line 600. Accordingly, reflected square-law detector415 is configured to receive the frequency-compensated sample ofreflected energy (RF voltage) representative of the reflected energytravelling on main transmission line 600, convert thefrequency-compensated sample of reflected energy to a reflected analogDC voltage representative of the reflected energy travelling on maintransmission line 600, and provide the reflected analog DC voltage toreflected analog gain stage 425. In one exemplary embodiment, thereflected analog DC voltage output can, at maximum full scale power,have a voltage of about 1 mV.

Forward analog gain stage 420 receives the forward analog DC voltagefrom the forward square-law detector 410, amplifies the forward analogDC voltage to a level sufficient for processing by the analog to digitalconverter (ADC) 430, thereby producing an amplified forward DC voltage.The forward analog gain stage 420 outputs the amplified forward DCvoltage to the ADC 430. Accordingly, the forward analog gain stage 420is configured to receive the forward analog DC voltage representative ofthe forward energy travelling on main transmission line 600, produce anamplified forward DC voltage having a level sufficient for processing bythe ADC 430 by amplifying the forward analog DC voltage, and output theamplified forward DC voltage to the ADC 430. In one exemplaryembodiment, the amplified forward DC voltage output can, at maximum fullscale power, have a voltage of about 1 V.

Reflected analog gain stage 425 receives the reflected analog DC voltagefrom the reflected square-law detector 415, amplifies the reflectedanalog DC voltage to a level sufficient for processing by ADC 430,thereby producing an amplified reflected DC voltage. The reflectedanalog gain stage 425 outputs the amplified reflected DC voltage to theADC 430. Accordingly, the reflected analog gain stage 425 is configuredto receive the reflected analog DC voltage representative of thereflected energy travelling on main transmission line 600, produce anamplified reflected DC voltage having a level sufficient for processingby the ADC 430 by amplifying the reflected analog DC voltage, and outputthe amplified reflected DC voltage to the ADC 430. In one exemplaryembodiment, the amplified reflected DC voltage output can, at maximumfull scale power, have a voltage of about 1 V.

The temperature sensor 405 is located in close proximity to the forwardsquare-law detector 410 and reflected square-law detector 415 andmeasures the ambient temperature in the proximity of the forwardsquare-law detector 410 and reflected square-law detector 415.Accordingly, temperature sensor 405 is configured to measure the ambienttemperature in the proximity of forward square-law detector 410 andreflected square-law detector 415 and provide a temperature level outputto the ADC 430 in the form of an analog DC voltage. The temperaturelevel output of temperature sensor 405 is then digitized and provided tomicrocontroller 435. In one exemplary embodiment, the temperature leveloutput can have a voltage of about 424 mVDC to 740 mVDC, from 0° C. to50° C.

The output of the forward square-law detector 410 and reflectedsquare-law detector 415 varies with the ambient temperature. Themicrocontroller 435 uses the temperature level output of temperaturesensor 405 in conjunction with the temperature characterization curve ofthe forward square-law detector 410 and reflected square-law detector415 stored in microcontroller 435 to compensate for the effects ofthermally induced drift in the forward square-law detector 410 andreflected square-law detector 415. Further, microcontroller 435 uses acalibration correction factor for each of the forward channel 301 andreflected channel 302 to help attain good absolute accuracy of measuredRF power to a NIST traceable standard. The calibration correction factorcorrects for any static variation from RF power sensor 100 to RF powersensor 100 in areas such as, but not limited to, coupling levels,losses, detector response, and amplifier gain.

In an exemplary embodiment, the forward channel 301 can include couplertransmission line section 251, coupled line 311, forward coupler sidearm 312, forward resistive attenuator 320, forward compensationcapacitor 330, forward square-law detector 410, forward analog gainstage 420, and analog to digital converter 430. The reflected channel302 can include coupler transmission line section 251, coupled line 311,reflected coupler side arm 314, reflected resistive attenuator 325,reflected compensation capacitor 335, reflected square-law detector 415,reflected analog gain stage 425, and analog to digital converter 430.The calibration correction factor for the forward channel 301 and thereflected channel 302 can be determined by the factory at the time ofmanufacture and stored in memory 437 of microcontroller 435.

ADC 430 receives the analog amplified forward DC voltage output from theforward analog gain stage 420, amplified reflected DC voltage outputfrom the reflected analog gain stage 425, and temperature level outputfrom temperature sensor 405. ADC 430 digitizes the analog amplifiedforward DC voltage output from the forward analog gain stage 420,amplified reflected DC voltage output from the reflected analog gainstage 425, and temperature level output from temperature sensor 405. ADC430 produces and outputs to microcontroller 435 values for the digitizedforward power (digitized amplified forward DC voltage output from theforward analog gain stage 420), digitized reflected power (digitizedamplified reflected DC voltage output from the reflected analog gainstage 425), and digitized temperature (digitized temperature leveloutput from temperature sensor 405).

Accordingly, ADC 430 is configured to receive and digitize the amplifiedforward DC voltage output from the forward analog gain stage 420 whichis representative of the forward energy travelling on main transmissionline 600, receive the amplified reflected DC voltage output from thereflected analog gain stage 425 which is representative of the reflectedenergy travelling on main transmission line 600, and temperature leveloutput from temperature sensor 405 which is representative of theambient air temperature around forward square-law detector 410 andreflected square-law detector 415, and output the digitized values forthe digitized forward power, digitized reflected power, and digitizedtemperature to microcontroller 435. Therefore, ADC 430 is configured toreceive the analog values for amplified forward DC voltage output fromthe forward analog gain stage 420, the amplified reflected DC voltageoutput from the reflected analog gain stage 425, and temperature leveloutput from temperature sensor 405, digitize the analog received values,and output the digitized values for the digitized forward power,digitized reflected power, and digitized temperature to microcontroller435.

Microcontroller 435 receives the digitized values for the digitizedforward power, digitized reflected power, and digitized temperatureoutput from ADC 430. Microcontroller 435 applies a temperaturecorrection and a calibration correction factor for the forward channel301 to the digitized forward power and outputs the corrected digitizedforward power to port 440 for output to channel power meter 720.Microcontroller 435 also applies the temperature correction and acalibration correction factor for the reflected channel 302 to digitizedreflected power, and outputs the corrected reflected power to port 440for output to channel power meter 720. The microcontroller 435 uses thetemperature level output of temperature sensor 405 in conjunction withthe temperature characterization curve of the forward square-lawdetector 410 and the temperature characterization curve of the reflectedsquare-law detector 415 stored in microcontroller 435 to apply atemperature correction to the digitized forward power and digitizedreflected power values received from ADC 430. The temperature correctionapplied by microcontroller 435 to the digitized forward power and thedigitized reflected power compensates for the effects of thermallyinduced drift in the forward square-law detector 410 and reflectedsquare-law detector 415. The calibration correction factors applied bymicrocontroller 435 correct for any static variation from RF powersensor 100 to RF power sensor 100 in areas such as, but not limited to,coupling levels, losses, detector response, and amplifier gain.

Further, microcontroller 435 also receives the output from reset switch445. Microcontroller 435 is also configured to restart when reset switch445 is pressed, which may be used to “wake-up” microcontroller 435should microcontroller 435 enter a sleep state. Microcontroller 435 isfurther configured to control the state of LED 450. In an exemplaryembodiment, microcontroller 435 is configured to illuminate LED 450 whenRF power sensor 100 is provided with electrical power through port 440.In another exemplary embodiment, microcontroller 435 is configured toilluminate LED 450 to indicate special conditions of RF power sensor 100such as, but not limited to, an alarm condition or communication error.

Port 440 receives the corrected digitized forward power and correctedreflected power from microcontroller 435 and provides them for output tochannel power meter 720. In an exemplary embodiment, port 440 providesthe corrected digitized forward power and corrected reflected powervalues to channel power meter 720 using serial communication. In anotherexemplary embodiment, microcontroller 435, through port 440, providesthe corrected digitized forward power and corrected reflected powervalues to channel power meter 720 using serial communication. However,it is contemplated that a person having ordinary skill in the art canchoose to provide the corrected digitized forward power and correctedreflected power values to channel power meter 720 using a form ofcommunication other than serial communication.

FIG. 14 is a block diagram of microcontroller 435, which includesprocessor 436 and memory 437. In some exemplary embodiments, ADC 430 isintegrated into microcontroller 435. Further, in some exemplaryembodiments, such as the one shown in FIG. 13, the ADC 430 andmicrocontroller 435 are not integrated. Further, since microcontroller435 includes a processor 436 and memory 437, the term microcontroller435 is intended to encompass embodiments of RF power sensor 100 that areimplemented using stand-alone processor 436 and memory 437, and alsoembodiments of RF power sensor 100 that are implemented using amicrocontroller 435 that has an integrated processor 436 and memory 437.

The program of FIG. 15 calculates the corrected digitized forward powerand corrected reflected power. The program of FIG. 15 is stored inmemory 437 and executed by processor 436, and is directed to a methodfor the calculation the forward and reflected power 1200 on transmissionline 600 using the processor 436 and memory 437 of microcontroller 435of RF power sensor 100.

In block 1205, the status of the reset switch 445 is examined. If thereset switch 445 is pressed, the method progresses to block 1210, wherethe microcontroller 435 is restarted or “wakes-up” if it has entered asleep mode. After the microcontroller 435 is restarted, the methodprogresses back to block 1205.

If the reset switch 445 is not pressed in block 1205, the methodprogresses to block 1215, where LED 450 is illuminated, indicating thatRF power sensor 100 is receiving electrical power. In one exemplaryembodiment, the electrical power for RF power sensor 100 is provided bychannel power meter 720 through port 440.

In an exemplary embodiment, processor 436 pauses before block 1220,until processor 436 receives a request for a measurement of forward andreflected power on main transmission line 600. In another exemplaryembodiment, processor 436 pauses before block 1220, until a measurementof forward and reflected power is requested by channel power meter 720.

In block 1220, the digitized values for digitized forward power,digitized reflected power, and digitized temperature output are receivedby processor 436 from ADC 430 and stored in memory 437. The temperaturecharacterization curve of the forward square-law detector 410, thecalibration correction factor for the forward channel 301, thetemperature characterization curve of the reflected square-law detector415, and the and calibration correction factor for the reflected channel302 are stored in memory 437 at the factory.

In block 1225, the corrected digitized forward power value and thecorrected digitized reflected power value are calculated by processor436. More specifically, the processor 436 retrieves the temperaturecharacterization curve of the forward square-law detector 410,calibration correction factor of the forward channel 301, digitizedvalue for the digital forward power, and the digitized temperatureoutput value from memory 437. Processor 436 calculates the correcteddigitized forward power value using the temperature characterizationcurve of the forward square-law detector 410, calibration correctionfactor of the forward channel 301, digitized value for the digitalforward power, and the digitized temperature output value. Processor 436stores the calculated corrected digitized forward power value in memory437.

Further, the processor 436 retrieves the temperature characterizationcurve of the reflected square-law detector 415, calibration correctionfactor of the reflected channel 302, digitized value for the digitalreflected power, and the digitized temperature output value from memory437. Processor 436 calculates the corrected digitized reflected powervalue using the temperature characterization curve of the forwardsquare-law detector 410, and calibration correction factor of thereflected channel 302, digitized value for the digital reflected power,and the digitized temperature output value. Processor 436 stores thecalculated corrected digitized reflected power value in memory 437.

In block 1230, processor 436 retrieves the calculated correcteddigitized forward power value and calculated corrected digitizedreflected power value from memory 437. Processor 436 outputs thecorrected digitized forward power value and corrected digitizedreflected power value to channel power meter 720 using port 440. Themethod then progresses back to block 1205.

FIGS. 19-20 are flow charts of a method 1100 of using RF power sensor100 in accordance with an exemplary embodiment of the invention. Inblock 1105, RF power sensor 100 and main transmission line 600 areprovided. In block 1110, RF power sensor 100 is connected to the maintransmission line 600.

In block 1115, a sample of forward energy and a sample of reflectedenergy from main transmission line 600 are obtained by RF power sensor100 using frequency compensated shortline directional coupler 300. Morespecifically, the coupler 305 and coupling structure 310 of directionalcoupler 300 obtain the sample of forward energy and the sample ofreflected energy. Even more specifically, coupled line 311 and forwardcoupler side arm 312 obtain the sample of forward energy from thecoupler transmission line section 251, and the coupled line 311 andreflected coupler side arm 314 obtain the sample of forward energy fromthe coupler transmission line section 251. The sample of forward energyis representative of the energy travelling on the main transmission line600 in the forward direction. The sample of reflected energy isrepresentative of the energy travelling on the main transmission line600 in the reflected direction.

In block 1120, forward resistive attenuator 320 attenuates the sample offorward energy using forward resistive attenuator 320, thereby producingan attenuated sample of forward energy. Further, reflected resistiveattenuator 325 attenuates the sample of reflected energy using reflectedresistive attenuator 325, thereby producing an attenuated sample ofreflected energy.

In block 1125, forward compensation capacitor 330 applies compensationto the attenuated sample of forward energy, thereby producing afrequency-compensated sample of forward energy. Further, reflectedcompensation capacitor 335 applies compensation to the attenuated sampleof reflected energy, thereby producing a frequency-compensated sample ofreflected energy.

In block 1130, power measurement circuit 400 converts thefrequency-compensated sample of forward energy into a correcteddigitized forward power representative of the forward energy travellingon the main transmission line 600. Further, power measurement circuit400 converts the frequency-compensated sample of reflected energy into acorrected digitized reflected power representative of the reflectedenergy travelling on the main transmission line 600.

In block 1135, power measurement circuit 400 outputs the correcteddigitized forward power and the corrected digitized reflected power. Inan exemplary embodiment, power measurement circuit 400 outputs thecorrected digitized forward power and the corrected digitized reflectedpower using port 440. In another exemplary embodiment, power measurementcircuit 400 outputs the corrected digitized forward power and thecorrected digitized reflected power using port 440 to channel powermeter 720.

Blocks 1130 a-1130 d of FIG. 20 provide additional details regarding theacts taking place in block 1130 of FIG. 19 by power measurement circuit400. In block 1130 a, the frequency-compensated sample of forward energyis converted by forward square-law detector 410 to a forward analog DCvoltage representative of the forward energy travelling on maintransmission line 600. Further, the frequency-compensated sample ofreflected energy is converted by reflected square-law detector 415 to areflected analog DC voltage representative of the reflected energytravelling on main transmission line 600.

In block 1130 b, the forward analog DC voltage is amplified by forwardanalog gain stage 420, thereby producing an amplified forward analog DCvoltage. Further, the reflected analog DC voltage is amplified byreflected analog gain stage 425, thereby producing an amplifiedreflected analog DC voltage.

In block 1130 c, the amplified forward analog DC voltage is digitized byADC 430 into a digitized forward power value, and the amplifiedreflected analog DC voltage is digitized by ADC 430 into a digitizedreflected power value.

In block 1130 d, a temperature correction and calibration correctionfactor are applied to the digitized forward power by microcontroller435, thereby producing the corrected digitized forward power that isoutputted by power measurement circuit 400 in block 1135. In anexemplary embodiment, the calibration correction factor applied to thedigitized forward power is a calibration correction factor for theforward channel 301. Further, a temperature correction and calibrationcorrection factor are applied to the digitized reflected power bymicrocontroller 435, thereby producing the corrected digitized reflectedpower that is outputted by power measurement circuit 400 in block 1135.In an exemplary embodiment, the calibration correction factor applied tothe digitized reflected power is a calibration correction factor for thereflected channel 302.

FIG. 21 shows a block diagram of channel power meter 720, which includesport 721, processor 722, memory 725, and User I/O 726. User I/O 726 caninclude one or both of user input device 723 and display 724. In someexemplary embodiments, display 724 and user input device 723 of user I/O726 can be combined, such as a touch screen. Further, user I/O 726 canhave a separate display 724 and user input device 723. In otherexemplary embodiments, user input device 723 can be buttons, a keypad orkeyboard.

Processor 722 is electrically connected to port 721, display 724, memory725, and user I/O 726. Channel power meter 720 is configured to receivea corrected digitized forward power from RF power sensor 100 and displayto a user, via display 724, the corresponding value of RF powertravelling in the forward direction on combined channel transmissionline 830. Channel power meter 720 is further configured to receive acorrected digitized reflected power from RF power sensor 100 and displayto a user, via display 724, the corresponding value of RF powertravelling in the reflected direction on combined channel transmissionline 830. A user can utilize user I/O 726 to display the individualvalues for RF power travelling in the forward and reflected directions,as well as the composite power, on combined channel transmission line830 as measured by RF power sensor 100. A user can also utilize user I/O726 to display the VSWR on combined channel transmission line 830.

FIG. 22 shows a block diagram of an RF power metering system 800 for anRF transmission system 801. RF power metering system 800 has a firstinput power sensor 810, second input power sensor 820, and output powersensor 835. RF transmission system 801 has a first channel transmissionline 805, second channel transmission line 815, combiner 825, andcombined channel transmission line 830.

First input power sensor 810 is electrically connectable to firstchannel transmission line 805 and channel power meter 720. Second inputpower sensor 820 is electrically connectable to second channeltransmission line 815 and channel power meter 720. Combiner 825 iselectrically connected to first channel transmission line 805, secondchannel transmission line 815, and combined channel transmission line830. Output power sensor 835 is electrically connectable to combinedchannel transmission line 830 and channel power meter 720.

First input power sensor 810 is configured to measure the RF power levelon the first channel transmission line 805 and provide the measured RFpower level on the first channel transmission line 805 to channel powermeter 720. Second input power sensor 820 is configured to measure the RFpower level on the second channel transmission line 815 and provide themeasured RF power level on the second channel transmission line 815 tochannel power meter 720. First input power sensor 810 can be adirectional or non-directional power sensor. Second input power sensor820 can be a directional or non-directional power sensor.

Combiner 825 is configured to combine the first channel from firstchannel transmission line 805 and the second channel from second channeltransmission line 815 onto combined channel transmission line 830.Output power sensor 835 is configured to measure the RF power level forthe first channel on the combined channel transmission line 830 andprovide the measured RF power level for the first channel to channelpower meter 720. Output power sensor 835 is further configured tomeasure the forward RF power level and reflected RF power level for thefirst channel on the combined channel transmission line 830 and providethe forward RF power level and reflected RF power level for the firstchannel to channel power meter 720. Output power sensor 835 is alsoconfigured to measure the RF power level for the second channel on thecombined channel transmission line 830 and provide the measured RF powerlevel for the second channel to channel power meter 720. Output powersensor 835 is further configured to measure the forward RF power leveland reflected RF power level for the second channel on the combinedchannel transmission line 830 and provide the forward RF power level andreflected RF power level for the second channel to channel power meter720.

Output power sensor 835 can be any device that is capable of determiningdirectional channelized power, such as a spectrum analyzer. Output powersensor 835 can also be a directional device that is not capable ofdetermining channelized power (e.g. a composite power measurementdevice), such as RF power sensor 100, as long as only the channel ofinterest is activated when the RF power level for the channel ofinterest is being measured. For example, a composite power measurementdevice can be used as output power sensor 835, if only the first channelis activated during the time the RF power level for the first channel isbeing measured, and only the second channel is activated during the timethe RF power level for the second channel is being measured.

Channel power meter 720 is configured to display the RF power level forthe first channel on the first channel transmission line 805, which isthe RF power level for the first channel pre-combiner (RF power levelfor the first channel before entering combiner 825). Channel power meter720 is also configured to display the RF power level for the secondchannel on the second channel transmission line 815, which is the RFpower level for the second channel pre-combiner (RF power level for thesecond channel before entering combiner 825). Additionally, channelpower meter 720 is configured to display the RF power level for thefirst channel on the combined channel transmission line 830, which isthe RF power level for the first channel post-combiner (RF power levelfor the first channel after exiting combiner 825). Further, channelpower meter 720 is configured to display the RF power level for thesecond channel on the combined channel transmission line 830, which isthe RF power level for the second channel post-combiner (RF power levelfor the second channel after exiting combiner 825). Further, channelpower meter 720 is configured to display the composite RF power level,which is the RF power level for all of the channels post-combiner on thecombined channel transmission line 830 (RF power level for all of thechannels after exiting combiner 825).

Additionally, channel power meter 720 is configured to display theforward RF power level for the first channel on the combined channeltransmission line 830, which is the RF power level for the first channelin the forward direction post-combiner (forward RF power level for thefirst channel after exiting combiner 825). Also, channel power meter 720is configured to display the reflected RF power level for the firstchannel on the combined channel transmission line 830, which is the RFpower level for the first channel in the reflected directionpost-combiner (reflected RF power level for the first channel afterexiting combiner 825). Further, channel power meter 720 is configured todisplay the forward RF power level for the second channel on thecombined channel transmission line 830, which is the forward RF powerlevel for the second channel post-combiner (forward RF power level forthe second channel after exiting combiner 825). Further, channel powermeter 720 is configured to display the reflected RF power level for thesecond channel on the combined channel transmission line 830, which isthe reflected RF power level for the second channel post-combiner(forward RF power level for the second channel after exiting combiner825). Further, channel power meter 720 is configured to display thecomposite RF power level, which is the RF power level for all of thechannels post-combiner on the combined channel transmission line 830 (RFpower level for all of the channels after exiting combiner 825).

Also, channel power meter 720 is configured to calculate and display thecombiner loss for the first channel, which is the difference between theRF power level for the first channel pre-combiner and the RF power levelfor the first channel post-combiner. Further, channel power meter 720 isconfigured to calculate and display the combiner loss for the secondchannel, which is the difference between the RF power level for thesecond channel pre-combiner and the RF power level for the secondchannel post-combiner. Additionally, channel power meter 720 isconfigured to calculate and display the voltage standing wave ratio(VSWR) on combined channel transmission line 830.

FIG. 23 is a flow chart showing a method 900 for determining combinerloss in the RF transmission system 801 using RF power metering system800. In block 905, a pre-combiner RF power level for the first channelon the first channel transmission line is measured using first inputpower sensor 810. In block 910, a post-combiner RF power level for thefirst channel on combined channel transmission line 830 is measuredusing output power sensor 835. In an exemplary embodiment, the postcombiner RF power level for the first channel is the forward RF powerlevel for the first channel travelling in a forward direction oncombined channel transmission line 830.

In block 915, a pre-combiner RF power level for the second channel onthe second channel transmission line 815 is measured using second inputpower sensor 820. In block 920, a post combiner RF power level for thesecond channel on combined channel transmission line 830 is measuredusing output power sensor 835. In an exemplary embodiment, the postcombiner RF power level for the second channel is the forward RF powerlevel for the second channel travelling in a forward direction oncombined channel transmission line 830.

Output power sensor 835 can also be a directional device that is notcapable of determining channelized power (e.g. a composite powermeasurement device), such as RF power sensor 100, as long as only thechannel of interest is activated when the RF power level for the channelof interest is being measured. For example, a composite powermeasurement device can be used as output power sensor 835, if only thefirst channel is activated during the time the RF power level for thefirst channel is being measured, and only the second channel isactivated during the time the RF power level for the second channel isbeing measured.

In block 925, the measured pre-combiner RF power level for the firstchannel is provided by first input power sensor 810 to channel powermeter 720, the measured post-combiner RF power level for the firstchannel is provided by output power sensor 835 to channel power meter720, the measured pre-combiner RF power level for the second channel isprovided by second input power sensor 820 to channel power meter 720,and the measured post-combiner RF power level for the second channel isprovided by output power sensor 835 to channel power meter 720.

In block 930, the combiner loss level for the first channel iscalculated using channel power meter 720, by calculating the differencebetween the pre-combiner RF power level for the first channel and thepost-combiner RF power level for the first channel.

In block 935, the combiner loss level for the second channel iscalculated, using channel power meter 720, by calculating the differencebetween the pre-combiner RF power level for the second channel and thepost-combiner RF power level for the second channel.

In block 940, the calculated combiner loss level for the first channeland the calculated combiner loss level for the second channel aredisplayed to the user by channel power meter 720. In an exemplaryembodiment, channel power meter 720 displays the calculated combinerloss level for the first channel and the calculated combiner loss levelfor the second channel using display 724 of user I/O 726.

FIG. 24 is a flowchart of a program 1000 for calculating loss in acombiner 825 stored in memory 725 and executed by processor 722 ofchannel power meter 720 in an exemplary embodiment of RF power meteringsystem 800, and will be described with reference to FIGS. 21-22.

In block 1005 a measured pre-combiner RF power level for a first channelis received by processor 722 and stored in memory 725. In some exemplaryembodiments, the measured pre-combiner RF power level for a firstchannel is received by channel power meter 720 in the form of a scaledDC voltage representative of the energy travelling on first channeltransmission line 805 (RF power level for the first channel beforeentering combiner 825). Measured pre-combiner RF power level for thefirst channel is measured by and received from first input power sensor810. The measured pre-combiner RF power level for the first channel isthe RF power level on the first channel transmission line 805.

In block 1010, a measured post-combiner RF power level for a firstchannel is received by processor 722 and stored in memory 725. Measuredpost-combiner RF power level for the first channel is measured by andreceived from output power sensor 835. In some exemplary embodiments,the measured post-combiner RF power level for a first channel is areceived by channel power meter 720 in the form of corrected digitizedforward power representative of the energy travelling in the forwarddirection on combined channel transmission line 830 for the firstchannel (RF power level for the first channel after exiting combiner825). In an exemplary embodiment, output power sensor 835 can be anydevice that is capable of determining directional channelized power,such as a spectrum analyzer. Output power sensor 835 can also be adirectional device that is not capable of determining directionalchannelized power (e.g. a composite power measurement device), such asRF power sensor 100, as long as only the channel of interest isactivated when the RF power level for the channel of interest is beingmeasured. For example, a composite power measurement device can be usedas output power sensor 835, if only the first channel is activatedduring the time the RF power level for the first channel is beingmeasured, and only the second channel is activated during the time theRF power level for the second channel is being measured. The measuredpost-combiner RF power level for the first channel is the RF power levelfor the first channel on combined channel transmission line 830.

In block 1015, a measured pre-combiner RF power level for a secondchannel is received by processor 722 and stored in memory 725. In someexemplary embodiments, the measured pre-combiner RF power level for asecond channel is a received by channel power meter 720 in the form of ascaled DC voltage representative of the energy travelling on secondchannel transmission line 815 (RF power level for the second channelbefore entering combiner 825). Measured pre-combiner RF power level forthe second channel is measured by and received from second input powersensor 820. Second input power sensor 820 can be a non-directional powersensor, such as RF power sensor 100. The measured pre-combiner RF powerlevel for the second channel is the RF power level on the second channeltransmission line 815.

In block 1020, a measured post-combiner RF power level for a secondchannel is received by processor 722 and stored in memory 725. In someexemplary embodiments, the measured post-combiner RF power level for asecond channel is a received by channel power meter 720 in the form ofcorrected digitized forward power representative of the energytravelling in the forward direction on combined channel transmissionline 830 for the second channel (RF power level for the second channelafter exiting combiner 825). Measured-post combiner RF power level forthe second channel is measured by and received from output power sensor835. In an exemplary embodiment, output power sensor 835 can be anydevice that is capable of determining directional channelized power,such as a spectrum analyzer. Output power sensor 835 can also be adirectional device that is not capable of determining channelized power(e.g. a composite power measurement device), such as RF power sensor100, as long as only the channel of interest is activated when the RFpower level for the channel of interest is being measured. For example,a composite power measurement device can be used as output power sensor835, if only the first channel is activated during the time the RF powerlevel for the first channel is being measured, and only the secondchannel is activated during the time the RF power level for the secondchannel is being measured. The measured post-combiner RF power level forthe second channel is the RF power level for the second channel oncombined channel transmission line 830.

In block 1025, a first channel combiner RF power loss level isdetermined by processor 722 by retrieving the measured pre-combiner RFpower level for the first channel from memory 725, retrieving themeasured post-combiner RF power level for the first channel from memory725, calculating the difference between the measured pre-combiner RFpower level for the first channel and the measured post-combiner RFpower level for the first channel, and storing the difference in memory725 as the first channel combiner RF power loss level.

In block 1030, a second channel combiner RF power loss level isdetermined by processor 722 by retrieving the measured pre-combiner RFpower level for the second channel from memory 725, retrieving themeasured post-combiner RF power level for the second channel from memory725, calculating the difference between the measured pre-combiner RFpower level for the second channel and the measured post-combiner RFpower level for the second channel, and storing the difference in memory725 as the second channel combiner RF power loss level.

In block 1035, the first channel combiner RF power loss level isretrieved from memory 725 by processor 722 and outputted to the user.Processor 722 can output the first channel combiner RF power loss levelto a user by utilizing user I/O 726. In an exemplary embodiment,processor 722 can output for display, the first channel combiner RFpower loss level to a user by utilizing display 724 of user I/O 726.

In block 1040, the second channel combiner RF power loss level isretrieved from memory 725 by processor 722 and outputted to the user.Processor 722 can output the second channel combiner RF power loss levelto a user by utilizing user I/O 726. In an exemplary embodiment,processor 722 can output for display, the second channel combiner RFpower loss level to a user by utilizing display 724 of user I/O 726.

In an exemplary embodiment, processor 722 can receive the measuredpre-combiner RF power level for the first channel, measuredpost-combiner RF power level for the first channel, measuredpre-combiner RF power level for the second channel, and measuredpost-combiner RF power level for the second channel through port 721 ofchannel power meter 720.

FIG. 25 is a flow chart showing a method 1300 for determining thevoltage standing wave ratio (VSWR) on the combined channel transmissionline 830 of RF transmission system 801 using RF power metering system800. In block 1305, a post-combiner forward RF power level on thecombined channel transmission line 830 is measured using the outputpower sensor 835. In block 1310, a post-combiner reflected RF powerlevel on the combined channel transmission line 830 is measured usingoutput power sensor 835. In an exemplary embodiment, output power sensor835 is RF power sensor 100.

In block 1315, the measured forward RF power level and the measuredreflected RF power level on the combined channel transmission line 830are provided by output power sensor 835 to a channel power meter 720.

In block 1320, the VSWR is calculated, using the channel power meter720, according to the following equation 1:

$\begin{matrix}{{VSWR} = \frac{1 + \sqrt{\frac{P_{R}}{P_{F}}}}{1 - \sqrt{\frac{P_{R}}{P_{F\;}}}}} & \left( {{equation}\mspace{14mu} 1} \right)\end{matrix}$

-   -   where, VSWR is the Voltage Standing Wave Ratio, P_(F) is the        forward RF power level, and P_(R) is the reflected RF power        level.

In block 1325, the calculated VSWR level on the combined channeltransmission line 830 is displayed to a user by channel power meter 720.In an exemplary embodiment, channel power meter 720 displays thecalculated VSWR level using display 724 of user I/O 726.

FIG. 26 is a flowchart of a program 1400 for calculating VSWR stored inmemory 725 and executed by processor 722 of channel power meter 720 inan exemplary embodiment of RF power metering system 800.

In block 1405, a measured post-combiner forward RF power level for thecombined channel transmission line 830 is received by processor 722 andstored in memory 725. In some embodiments, the measured post-combinerforward RF power level for the combined channel transmission line 830 ismeasured by and received from the output power sensor 835. In anexemplary embodiment, output power sensor 835 can be RF power sensor100.

In block 1410, a measured post-combiner reflected RF power level for thecombined channel transmission line 830 is received by processor 722 andstored in memory 725. In some embodiments, the measured post-combinerreflected RF power level for the combined channel transmission line 830is measured by and received from the output power sensor 835.

In block 1415, the VSWR level on the combined channel transmission line830 is determined by processor 722 by retrieving the measuredpost-combiner forward RF power level and the measured post-combinerreflected RF power level from memory 725, calculating the VSWR levelusing equation 1 shown above, and storing the VSWR level in memory 725.

In block 1420, the VSWR level on the combined channel transmission line830 is retrieved from memory 725 by processor 722 and outputted to theuser. Processor 722 can output the VSWR level to a user by utilizinguser I/O 726. In an exemplary embodiment, processor 722 can output fordisplay, the VSWR level on the combined channel transmission line 830 toa user by utilizing display 724 of user I/O 726.

While this invention has been described in conjunction with the specificembodiments described above, it is evident that many alternatives,combinations, modifications and variations are apparent to those skilledin the art. Accordingly, the preferred embodiments of this invention, asset forth above are intended to be illustrative only, and not in alimiting sense. Various changes can be made without departing from thespirit and scope of this invention. Combinations of the aboveembodiments and other embodiments will be apparent to those of skill inthe art upon studying the above description and are intended to beembraced therein. Therefore, the scope of the present invention isdefined by the appended claims, and all devices, processes, and methodsthat come within the meaning of the claims, either literally or byequivalence, are intended to be embraced therein.

The invention claimed is:
 1. A directional coupler, comprising: acoupler, a forward resistive attenuator, a reflected resistiveattenuator, a forward compensation capacitor, and a reflectedcompensation capacitor; said coupler is comprised of a couplertransmission line section and a coupling structure; said couplingstructure has a coupled line with a coupling length of D1, said couplingstructure also has a forward coupler side arm electrically connected toan upstream end of said coupled line, and a reflected coupler side armelectrically connected to a downstream end of said coupled line; saidcoupling structure is a microstrip on a printed circuit board (PCB);said coupled line is coupled to said coupler transmission line section;said coupler transmission line section is a rigid air coaxialtransmission line electrically connected to an upstream connector and adownstream connector; said upstream connector and said downstreamconnector are mounted on an outer conductor; said outer conductor ismounted to said PCB; said forward coupler side arm is configured toobtain a sample of forward energy from said coupler transmission linesection using said coupled line, and said reflected coupler side arm isconfigured to obtain a sample of reflected energy from said coupledtransmission line section using said coupled line; said forward couplerside arm is electrically connected to said forward resistive attenuatorand configured to provide said sample of forward energy to said forwardresistive attenuator; said forward resistive attenuator is configured toattenuate said sample of forward energy, thereby producing an attenuatedsample of forward energy, said forward resistive attenuator iselectrically connected to said forward compensation capacitor andconfigured to provide said attenuated sample of forward energy to saidforward compensation capacitor; said forward compensation capacitor isconfigured to receive said attenuated sample of forward energy andproduce a frequency-compensated sample of forward energy; said reflectedcoupler side arm is electrically connected to said reflected resistiveattenuator and configured to provide said sample of reflected energy tosaid reflected resistive attenuator; said reflected resistive attenuatoris configured to attenuate said sample of reflected energy, therebyproducing an attenuated sample of reflected energy, said reflectedresistive attenuator is electrically connected to said reflectedcompensation capacitor and configured to provide said attenuated sampleof reflected energy to said reflected compensation capacitor; and saidreflected compensation capacitor is configured to receive saidattenuated sample of reflected energy and produce afrequency-compensated sample of reflected energy.
 2. The directionalcoupler as set forth in claim 1, wherein said directional coupler isconfigured as a frequency-compensated shortline dual directionalcoupler.
 3. The directional coupler as set forth in claim 1, whereinsaid coupling length (D1) of said coupled line is less than λ/4, where λis a wavelength of an RF wave in said coupled line at a center frequencyof said directional coupler.
 4. The directional coupler as set forth inclaim 1, wherein said coupling length (D1) of said coupled line isbetween λ/32 and λ/64.
 5. The directional coupler as set forth in claim4, wherein said coupling length (D1) of said coupled line is λ/42. 6.The directional coupler as set forth in claim 1, wherein said forwardcompensation capacitor is configured as: a shunt capacitor, a feedthrushunt capacitor, a capacitive divider having a series capacitor and saidshunt capacitor, said capacitive divider having said series capacitorand said feedthru shunt capacitor, or said capacitive divider having afirst shunt capacitor and said series capacitor and a second shuntcapacitor, wherein said second shunt capacitor is said feedthru shuntcapacitor.
 7. The directional coupler as set forth in claim 1, whereinsaid reflected compensation capacitor is configured as: a shuntcapacitor, a feedthru shunt capacitor, a capacitive divider having aseries capacitor and said shunt capacitor, said capacitive dividerhaving said series capacitor and said feedthru shunt capacitor, or saidcapacitive divider having a first shunt capacitor and said seriescapacitor and a second shunt capacitor, wherein said second shuntcapacitor is said feedthru shunt capacitor.
 8. The directional coupleras set forth in claim 1, wherein: said forward resistive attenuator iscomprised of a first chip attenuator and said reflected attenuator iscomprised of a second chip attenuator, or said forward resistiveattenuator is comprised of said first chip attenuator and a first lumpedattenuator, and said reflected attenuator is comprised of said secondchip attenuator and a second lumped attenuator.
 9. The directionalcoupler as set forth in claim 1, wherein: said forward compensationcapacitor and said reflected compensation capacitor are configured to:reduce the coupling of said coupled line to said coupler transmissionline section, thereby flattening a frequency response of saiddirectional coupler, and/or reduce a level of said frequency-compensatedsample of forward energy and a level of said frequency-compensatedsample of reflected energy through voltage division and reduce animpedance seen by a forward square-law detector and a reflectedsquare-law detector; and/or said forward resistive attenuator providesisolation between said forward compensation capacitor and said couplingstructure, and said reflected resistive attenuator provides isolationbetween said reflected compensation capacitor and said couplingstructure, thereby preventing said forward compensation capacitor andsaid reflected compensation capacitor from degrading a directivity ofsaid coupler structure.
 10. A radio frequency (RF) power sensorcomprising: a directional coupler and a power measurement circuit; saiddirectional coupler is configured to sample energy on a maintransmission line and provides a frequency-compensated sample of forwardenergy and a frequency-compensated sample of reflected energy to saidpower measurement circuit; said frequency-compensated sample of forwardenergy is a sample of energy travelling in the forward direction on saidmain transmission line, and said frequency-compensated sample ofreflected energy is a sample of energy travelling in the reflecteddirection on said main transmission line; said power measurement circuitis configured to receive said frequency-compensated sample of forwardenergy and said frequency-compensated sample of reflected energy andoutput a corrected digitized forward power that is representative of theforward energy travelling on said main transmission line, and acorrected digitized reflected power which is representative of thereflected energy travelling on said main transmission line; saiddirectional coupler comprises a coupler, a forward resistive attenuator,a reflected resistive attenuator, a forward compensation capacitor, anda reflected compensation capacitor; said coupler is comprised of acoupler transmission line section and a coupling structure; saidcoupling structure has a coupled line with a coupling length of D1, saidcoupling structure also has a forward coupler side arm electricallyconnected to an upstream end of said coupled line, and a reflectedcoupler side arm electrically connected to a downstream end of saidcoupled line; said coupling structure is a microstrip on a printedcircuit board (PCB); said coupled line is coupled to said couplertransmission line section; said coupler transmission line section is arigid air coaxial transmission line; said forward coupler side arm isconfigured to obtain a sample of forward energy from said couplertransmission line section using said coupled line, and said reflectedcoupler side arm is configured to obtain a sample of reflected energyfrom said coupled transmission line section using said coupled line;said forward coupler side arm is electrically connected to said forwardresistive attenuator and configured to provide said sample of forwardenergy to said forward resistive attenuator; said forward resistiveattenuator is configured to attenuate said sample of forward energy,thereby producing an attenuated sample of forward energy, said forwardresistive attenuator is electrically connected to said forwardcompensation capacitor and configured to provide said attenuated sampleof forward energy to said forward compensation capacitor; said forwardcompensation capacitor is configured to receive said attenuated sampleof forward energy and produce a frequency-compensated sample of forwardenergy; said reflected coupler side arm is electrically connected tosaid reflected resistive attenuator and configured to provide saidsample of reflected energy to said reflected resistive attenuator; saidreflected resistive attenuator is configured to attenuate said sample ofreflected energy, thereby producing an attenuated sample of reflectedenergy, said reflected resistive attenuator is electrically connected tosaid reflected compensation capacitor and configured to provide saidattenuated sample of reflected energy to said reflected compensationcapacitor; and said reflected compensation capacitor is configured toreceive said attenuated sample of reflected energy and produce afrequency-compensated sample of reflected energy.
 11. The RF powersensor as set forth in claim 10, wherein said directional coupler isconfigured as a frequency-compensated shortline dual directionalcoupler.
 12. The RF power sensor as set forth in claim 10, wherein saidcoupling length (D1) of said coupled line is less than λ/4, where λ is awavelength of an RF wave in said coupled line at a center frequency ofsaid directional coupler.
 13. The RF power sensor as set forth in claim10, wherein said coupling length (D1) of said coupled line is betweenλ/32 and λ/64.
 14. The RF power sensor as set forth in claim 13, whereinsaid coupling length (D1) of said coupled line is λ/42.
 15. The RF powersensor as set forth in claim 10, wherein said forward compensationcapacitor is configured as: a shunt capacitor, a feedthru shuntcapacitor, a capacitive divider having a series capacitor and said shuntcapacitor, said capacitive divider having said series capacitor and saidfeedthru shunt capacitor, or said capacitive divider having a firstshunt capacitor and said series capacitor and a second shunt capacitor,wherein said second shunt capacitor is said feedthru shunt capacitor.16. The RF power sensor as set forth in claim 10, wherein said reflectedcompensation capacitor is configured as: a shunt capacitor, a feedthrushunt capacitor, a capacitive divider having a series capacitor and saidshunt capacitor, said capacitive divider having said series capacitorand said feedthru shunt capacitor, or said capacitive divider having afirst shunt capacitor and said series capacitor and a second shuntcapacitor, wherein said second shunt capacitor is said feedthru shuntcapacitor.
 17. The RF power sensor as set forth in claim 10, wherein:said forward resistive attenuator is comprised of a first chipattenuator and said reflected attenuator is comprised of a second chipattenuator, or said forward resistive attenuator is comprised of saidfirst chip attenuator and a first lumped attenuator, and said reflectedattenuator is comprised of said second chip attenuator and a secondlumped attenuator.
 18. The RF power sensor as set forth in claim 10,wherein: said forward compensation capacitor and said reflectedcompensation capacitor are configured to: reduce the coupling of saidcoupled line to said coupler transmission line section, therebyflattening a frequency response of said directional coupler, and/orreduce a level of said frequency-compensated sample of forward energyand a level of said frequency-compensated sample of reflected energythrough voltage division and reduce an impedance seen by a forwardsquare-law detector and a reflected square-law detector; and/or saidforward resistive attenuator provides isolation between said forwardcompensation capacitor and said coupling structure, and said reflectedresistive attenuator provides isolation between said reflectedcompensation capacitor and said coupling structure, thereby preventingsaid forward compensation capacitor and said reflected compensationcapacitor from degrading a directivity of said coupler structure.